The present invention is directed to an improved design of a joint cover for use, particularly on pressurized telecommunication cables.
It is occasionally necessary to repair telecommunication cables and other cables. Since a repair involves the removal of some of the protective cable sheath, it is, therefore, necessary to provide the resultant joint with a cover having excellent resistance to moisture ingress and resistance to mechanical damage, ideally for the life of the cable.
It is possible to provide protection against moisture ingress to telecommunication cable joints by providing a wrap-around, heat-shrinkable sleeve and by placing this sleeve so that it is wrapped around the joint and also extends some way along the entrance and exit cables. An example of such an arrangement is disclosed in British Patent Specification 1,506,242. The longitudinal edges of the sleeve are fastened tightly together by means of a flexible C-shaped metal channel or clip. On heating with a propane flame, for example, the sleeve will shrink and, together with an adhesive which is on the interior surface, forms a water-tight cover over the joint. The effectiveness of such a joint cover may be assessed by pressurizing the cover to about 6 psi with air and thermally cycling the pressurized joint cover in water from 5.degree. C. to 60.degree. C. The pressure loss for satisfactory joints should not exceed 1 psi after 10 cycles, with each cycle being of a duration of four hours. This type of a test is carried out to evaluate joint covers used on distribution cables, even though the cables ar not normally pressurized.
In the case of telecommunication transmission systems, the cables are usually permanently pressurized to 10 psi to ensure that, even in the event of damage, water will be kept out. The suitability of the repair joint cover for use on transmission lines may be assessed by pressurizing the cover to 10 psi and then cycling the pressurized cover between -40.degree. C. and 60.degree. C. in air. No measurable pressure loss should occur after 10 cycles, with each cycle having a duration of 8 hours. Other thermal cycling tests for assessing the air retention effectiveness by these joint covers are used. A further requirement and, particularly, demanding one is that the pressurized joint cover should have excellent creep resistance so that it does not move or distort, ideally for the life of the cable.
To meet the exacting requirements for joint covers to be used on pressurized telecommunication cables, many systems have been used. For example, iron sections have been bolted together around the joint together with collars and adhesive coated tapes used to seal the inlet and outlet cables. This type of cover joint has the drawbacks of being rigid and being difficult to assemble. Also, this type of joint cover, which needs a large number of different size components to cater for the range of cable size being used, thus, requires a large amount of storage space, which can prove inconvenient.